#!/usr/bin/perl

use warnings 'all';
use strict;

sub my_sub {1}

foreach my $sub (qw /my_sub no_sub/) {
    print "$sub ", defined &$sub ? "exists\n" : "doesn't exist\n";
}

__END__
my_sub exists
no_sub doesn't exist
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print "my_sub ", test_for_sub("my_sub") ? "exists\n" : "doesn't exist\
+n";
print "no_sub ", test_for_sub("no_sub") ? "exists\n" : "doesn't exist\
+n";

sub test_for_sub {
        my ($expr) = @_;
        return eval "defined &$expr";
}

sub my_sub { 1; }
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